OK, I tried Okami in the PS3 and it seemed to play fine. The sound was a little jerky at the beginning but seemed to sort itself out. I didn't see anything that looked obviously like a graphical impediment. Having sat through the 20 minute opening sequence, I wasn't really looking forward to doing it all again on the PS2. But a faulty Game component cable solved that problem for me. Turned on the PS2 to see just flickering "AV3". I thought at first it was the switchbox I bought, but my xbox works fine via that. The Game component cable doesn't work plugged straight into the tv, so it's going back tomorrow.
Sorry I have no comparison comments, but like I say, I didn't see anything obvious on the PS3 that could be categorised as the "minor issue".
From other things I have read online, the US PS3 had an issue with the game which resulted in menus/in game dialogue subtitles being mirrored across the screen. I didn't see anything like that.
When I get a working comp cable from Game, or if I switch back to SCART, I'll let you know if the intro looks vastly different on PS2. Yes, even if it looks worse.
Edit: what am I talking about? One block on the BC list = noticeable issues, which is what Okami is meant to have. Primal has two blocks, minor issues.
So anyway, I definitely didn't see anything that seemed visually noticeable, which makes me wonder if the issue is in gameplay, menus etc. Saving, probably. :D